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<pre><span class="sourceLineNo">001</span><a name="line.1"></a>
<span class="sourceLineNo">002</span>/*<a name="line.2"></a>
<span class="sourceLineNo">003</span> * Copyright (C) 2014 Archie L. Cobbs. All rights reserved.<a name="line.3"></a>
<span class="sourceLineNo">004</span> *<a name="line.4"></a>
<span class="sourceLineNo">005</span> * $Id: SnapshotKVDatabase.html 939 2015-05-29 01:16:17Z archie.cobbs $<a name="line.5"></a>
<span class="sourceLineNo">006</span> */<a name="line.6"></a>
<span class="sourceLineNo">007</span><a name="line.7"></a>
<span class="sourceLineNo">008</span>package org.jsimpledb.kv.mvcc;<a name="line.8"></a>
<span class="sourceLineNo">009</span><a name="line.9"></a>
<span class="sourceLineNo">010</span>import java.util.ArrayList;<a name="line.10"></a>
<span class="sourceLineNo">011</span>import java.util.Iterator;<a name="line.11"></a>
<span class="sourceLineNo">012</span>import java.util.Map;<a name="line.12"></a>
<span class="sourceLineNo">013</span>import java.util.TreeMap;<a name="line.13"></a>
<span class="sourceLineNo">014</span><a name="line.14"></a>
<span class="sourceLineNo">015</span>import org.jsimpledb.kv.KVDatabase;<a name="line.15"></a>
<span class="sourceLineNo">016</span>import org.jsimpledb.kv.KVStore;<a name="line.16"></a>
<span class="sourceLineNo">017</span>import org.jsimpledb.kv.KVTransaction;<a name="line.17"></a>
<span class="sourceLineNo">018</span>import org.jsimpledb.kv.KVTransactionException;<a name="line.18"></a>
<span class="sourceLineNo">019</span>import org.jsimpledb.kv.RetryTransactionException;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import org.slf4j.Logger;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import org.slf4j.LoggerFactory;<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>/**<a name="line.23"></a>
<span class="sourceLineNo">024</span> * Multi-version conccurrency control (MVCC) database using snapshot views of an underlying {@link AtomicKVStore}.<a name="line.24"></a>
<span class="sourceLineNo">025</span> *<a name="line.25"></a>
<span class="sourceLineNo">026</span> * &lt;p&gt;<a name="line.26"></a>
<span class="sourceLineNo">027</span> * This class provides a {@link KVDatabase} view of an underlying {@link AtomicKVStore},<a name="line.27"></a>
<span class="sourceLineNo">028</span> * supporting concurrent transactions via MVCC and linearizable ACID semantics.<a name="line.28"></a>
<span class="sourceLineNo">029</span> * &lt;/p&gt;<a name="line.29"></a>
<span class="sourceLineNo">030</span> *<a name="line.30"></a>
<span class="sourceLineNo">031</span> * &lt;p&gt;<a name="line.31"></a>
<span class="sourceLineNo">032</span> * Instances implement a simple optimistic locking scheme for MVCC using {@link AtomicKVStore#snapshot}. Concurrent transactions<a name="line.32"></a>
<span class="sourceLineNo">033</span> * do not contend for any locks until commit time. During each transaction, reads are noted and derive from the snapshot,<a name="line.33"></a>
<span class="sourceLineNo">034</span> * while writes are batched up. At commit time, if any other transaction has committed writes since the transaction's<a name="line.34"></a>
<span class="sourceLineNo">035</span> * snapshot was created, and any of those writes {@linkplain Reads#isConflict conflict} with any of the committing<a name="line.35"></a>
<span class="sourceLineNo">036</span> * transaction's reads, a {@link RetryTransactionException} is thrown. Otherwise, the transaction is committed and its<a name="line.36"></a>
<span class="sourceLineNo">037</span> * writes are applied.<a name="line.37"></a>
<span class="sourceLineNo">038</span> * &lt;/p&gt;<a name="line.38"></a>
<span class="sourceLineNo">039</span> *<a name="line.39"></a>
<span class="sourceLineNo">040</span> * &lt;p&gt;<a name="line.40"></a>
<span class="sourceLineNo">041</span> * Each outstanding transaction's mutations are batched up in memory using a {@link Writes} instance. Therefore, the<a name="line.41"></a>
<span class="sourceLineNo">042</span> * transaction load supported by this class is limited to what can fit in memory.<a name="line.42"></a>
<span class="sourceLineNo">043</span> * &lt;/p&gt;<a name="line.43"></a>
<span class="sourceLineNo">044</span> */<a name="line.44"></a>
<span class="sourceLineNo">045</span>public class SnapshotKVDatabase implements KVDatabase {<a name="line.45"></a>
<span class="sourceLineNo">046</span><a name="line.46"></a>
<span class="sourceLineNo">047</span>// Locking order: (1) SnapshotKVTransaction, (2) SnapshotKVDatabase<a name="line.47"></a>
<span class="sourceLineNo">048</span><a name="line.48"></a>
<span class="sourceLineNo">049</span>    protected final Logger log = LoggerFactory.getLogger(this.getClass());<a name="line.49"></a>
<span class="sourceLineNo">050</span><a name="line.50"></a>
<span class="sourceLineNo">051</span>    private final TreeMap&lt;Long, SnapshotVersion&gt; versionInfoMap = new TreeMap&lt;&gt;();<a name="line.51"></a>
<span class="sourceLineNo">052</span><a name="line.52"></a>
<span class="sourceLineNo">053</span>    private AtomicKVStore kvstore;<a name="line.53"></a>
<span class="sourceLineNo">054</span>    private long currentVersion;<a name="line.54"></a>
<span class="sourceLineNo">055</span><a name="line.55"></a>
<span class="sourceLineNo">056</span>// Constructors<a name="line.56"></a>
<span class="sourceLineNo">057</span><a name="line.57"></a>
<span class="sourceLineNo">058</span>    /**<a name="line.58"></a>
<span class="sourceLineNo">059</span>     * Default constructor.<a name="line.59"></a>
<span class="sourceLineNo">060</span>     *<a name="line.60"></a>
<span class="sourceLineNo">061</span>     * &lt;p&gt;<a name="line.61"></a>
<span class="sourceLineNo">062</span>     * The underlying key/value store must still be configured before creating any transactions.<a name="line.62"></a>
<span class="sourceLineNo">063</span>     */<a name="line.63"></a>
<span class="sourceLineNo">064</span>    public SnapshotKVDatabase() {<a name="line.64"></a>
<span class="sourceLineNo">065</span>    }<a name="line.65"></a>
<span class="sourceLineNo">066</span><a name="line.66"></a>
<span class="sourceLineNo">067</span>    /**<a name="line.67"></a>
<span class="sourceLineNo">068</span>     * Constructor.<a name="line.68"></a>
<span class="sourceLineNo">069</span>     *<a name="line.69"></a>
<span class="sourceLineNo">070</span>     * @param kvstore underlying key/value store<a name="line.70"></a>
<span class="sourceLineNo">071</span>     */<a name="line.71"></a>
<span class="sourceLineNo">072</span>    public SnapshotKVDatabase(AtomicKVStore kvstore) {<a name="line.72"></a>
<span class="sourceLineNo">073</span>        this.kvstore = kvstore;<a name="line.73"></a>
<span class="sourceLineNo">074</span>    }<a name="line.74"></a>
<span class="sourceLineNo">075</span><a name="line.75"></a>
<span class="sourceLineNo">076</span>// Properties<a name="line.76"></a>
<span class="sourceLineNo">077</span><a name="line.77"></a>
<span class="sourceLineNo">078</span>    /**<a name="line.78"></a>
<span class="sourceLineNo">079</span>     * Get the underlying {@link AtomicKVStore}.<a name="line.79"></a>
<span class="sourceLineNo">080</span>     *<a name="line.80"></a>
<span class="sourceLineNo">081</span>     * @return underlying key/value store<a name="line.81"></a>
<span class="sourceLineNo">082</span>     */<a name="line.82"></a>
<span class="sourceLineNo">083</span>    protected synchronized AtomicKVStore getKVStore() {<a name="line.83"></a>
<span class="sourceLineNo">084</span>        return this.kvstore;<a name="line.84"></a>
<span class="sourceLineNo">085</span>    }<a name="line.85"></a>
<span class="sourceLineNo">086</span><a name="line.86"></a>
<span class="sourceLineNo">087</span>    /**<a name="line.87"></a>
<span class="sourceLineNo">088</span>     * Configure the underlying {@link AtomicKVStore}.<a name="line.88"></a>
<span class="sourceLineNo">089</span>     *<a name="line.89"></a>
<span class="sourceLineNo">090</span>     * &lt;p&gt;<a name="line.90"></a>
<span class="sourceLineNo">091</span>     * Required property; must be configured before creating any transactions.<a name="line.91"></a>
<span class="sourceLineNo">092</span>     *<a name="line.92"></a>
<span class="sourceLineNo">093</span>     * @param kvstore underlying key/value store<a name="line.93"></a>
<span class="sourceLineNo">094</span>     * @throws IllegalStateException if there are any transactions open<a name="line.94"></a>
<span class="sourceLineNo">095</span>     */<a name="line.95"></a>
<span class="sourceLineNo">096</span>    protected synchronized void setKVStore(AtomicKVStore kvstore) {<a name="line.96"></a>
<span class="sourceLineNo">097</span>        if (!this.versionInfoMap.isEmpty())<a name="line.97"></a>
<span class="sourceLineNo">098</span>            throw new IllegalStateException("transactions exist");<a name="line.98"></a>
<span class="sourceLineNo">099</span>        this.kvstore = kvstore;<a name="line.99"></a>
<span class="sourceLineNo">100</span>    }<a name="line.100"></a>
<span class="sourceLineNo">101</span><a name="line.101"></a>
<span class="sourceLineNo">102</span>// KVDatabase<a name="line.102"></a>
<span class="sourceLineNo">103</span><a name="line.103"></a>
<span class="sourceLineNo">104</span>    /**<a name="line.104"></a>
<span class="sourceLineNo">105</span>     * Create a new transaction.<a name="line.105"></a>
<span class="sourceLineNo">106</span>     *<a name="line.106"></a>
<span class="sourceLineNo">107</span>     * @throws IllegalStateException if no {@link AtomicKVStore} is configured<a name="line.107"></a>
<span class="sourceLineNo">108</span>     */<a name="line.108"></a>
<span class="sourceLineNo">109</span>    @Override<a name="line.109"></a>
<span class="sourceLineNo">110</span>    public synchronized KVTransaction createTransaction() {<a name="line.110"></a>
<span class="sourceLineNo">111</span><a name="line.111"></a>
<span class="sourceLineNo">112</span>        // Sanity check<a name="line.112"></a>
<span class="sourceLineNo">113</span>        if (this.kvstore == null)<a name="line.113"></a>
<span class="sourceLineNo">114</span>            throw new IllegalStateException("no KVSTore configured");<a name="line.114"></a>
<span class="sourceLineNo">115</span><a name="line.115"></a>
<span class="sourceLineNo">116</span>        // Get info for the current version<a name="line.116"></a>
<span class="sourceLineNo">117</span>        final SnapshotVersion versionInfo = this.getCurrentSnapshotVersion();<a name="line.117"></a>
<span class="sourceLineNo">118</span><a name="line.118"></a>
<span class="sourceLineNo">119</span>        // Create the new transaction and associate it with the current version<a name="line.119"></a>
<span class="sourceLineNo">120</span>        final SnapshotKVTransaction tx = this.createSnapshotKVTransaction(versionInfo);<a name="line.120"></a>
<span class="sourceLineNo">121</span>        versionInfo.addOpenTransaction(tx);<a name="line.121"></a>
<span class="sourceLineNo">122</span>        if (this.log.isDebugEnabled())<a name="line.122"></a>
<span class="sourceLineNo">123</span>            this.log.debug("created new transaction " + tx);<a name="line.123"></a>
<span class="sourceLineNo">124</span>        if (this.log.isTraceEnabled())<a name="line.124"></a>
<span class="sourceLineNo">125</span>            this.log.trace("updated current version info: " + versionInfo);<a name="line.125"></a>
<span class="sourceLineNo">126</span><a name="line.126"></a>
<span class="sourceLineNo">127</span>        // Done<a name="line.127"></a>
<span class="sourceLineNo">128</span>        return tx;<a name="line.128"></a>
<span class="sourceLineNo">129</span>    }<a name="line.129"></a>
<span class="sourceLineNo">130</span><a name="line.130"></a>
<span class="sourceLineNo">131</span>// Subclass methods<a name="line.131"></a>
<span class="sourceLineNo">132</span><a name="line.132"></a>
<span class="sourceLineNo">133</span>    /**<a name="line.133"></a>
<span class="sourceLineNo">134</span>     * Instantiate a new {@link SnapshotKVTransaction} instance.<a name="line.134"></a>
<span class="sourceLineNo">135</span>     *<a name="line.135"></a>
<span class="sourceLineNo">136</span>     * &lt;p&gt;<a name="line.136"></a>
<span class="sourceLineNo">137</span>     * The implementation in {@link SnapshotKVDatabase} just invokes the {@link SnapshotKVTransaction}<a name="line.137"></a>
<span class="sourceLineNo">138</span>     * constructor using {@code this} and {@code versionInfo}. Subclasses may want to override this method<a name="line.138"></a>
<span class="sourceLineNo">139</span>     * to create a more specific subclass.<a name="line.139"></a>
<span class="sourceLineNo">140</span>     *<a name="line.140"></a>
<span class="sourceLineNo">141</span>     * @param versionInfo associated snapshot info<a name="line.141"></a>
<span class="sourceLineNo">142</span>     * @return new transaction instance<a name="line.142"></a>
<span class="sourceLineNo">143</span>     * @throws KVTransactionException if an error occurs<a name="line.143"></a>
<span class="sourceLineNo">144</span>     */<a name="line.144"></a>
<span class="sourceLineNo">145</span>    protected SnapshotKVTransaction createSnapshotKVTransaction(SnapshotVersion versionInfo) {<a name="line.145"></a>
<span class="sourceLineNo">146</span>        return new SnapshotKVTransaction(this, versionInfo);<a name="line.146"></a>
<span class="sourceLineNo">147</span>    }<a name="line.147"></a>
<span class="sourceLineNo">148</span><a name="line.148"></a>
<span class="sourceLineNo">149</span>    /**<a name="line.149"></a>
<span class="sourceLineNo">150</span>     * Forcibly close all outstanding transactions.<a name="line.150"></a>
<span class="sourceLineNo">151</span>     *<a name="line.151"></a>
<span class="sourceLineNo">152</span>     * &lt;p&gt;<a name="line.152"></a>
<span class="sourceLineNo">153</span>     * Can be used by subclasses during the shutdown sequence to ensure everything is properly cleaned up.<a name="line.153"></a>
<span class="sourceLineNo">154</span>     * To avoid a possible lock order reversal deadlock, this instance should &lt;b&gt;not&lt;/b&gt; be locked when invoking this method.<a name="line.154"></a>
<span class="sourceLineNo">155</span>     */<a name="line.155"></a>
<span class="sourceLineNo">156</span>    protected void closeTransactions() {<a name="line.156"></a>
<span class="sourceLineNo">157</span><a name="line.157"></a>
<span class="sourceLineNo">158</span>        // Grab all remaining open transactions<a name="line.158"></a>
<span class="sourceLineNo">159</span>        final ArrayList&lt;SnapshotKVTransaction&gt; openTransactions = new ArrayList&lt;&gt;();<a name="line.159"></a>
<span class="sourceLineNo">160</span>        synchronized (this) {<a name="line.160"></a>
<span class="sourceLineNo">161</span>            for (SnapshotVersion versionInfo : this.versionInfoMap.values())<a name="line.161"></a>
<span class="sourceLineNo">162</span>                openTransactions.addAll(versionInfo.getOpenTransactions());<a name="line.162"></a>
<span class="sourceLineNo">163</span>        }<a name="line.163"></a>
<span class="sourceLineNo">164</span><a name="line.164"></a>
<span class="sourceLineNo">165</span>        // Close them (but not while holding my lock, to avoid lock order reversal)<a name="line.165"></a>
<span class="sourceLineNo">166</span>        for (SnapshotKVTransaction tx : openTransactions) {<a name="line.166"></a>
<span class="sourceLineNo">167</span>            try {<a name="line.167"></a>
<span class="sourceLineNo">168</span>                tx.rollback();<a name="line.168"></a>
<span class="sourceLineNo">169</span>            } catch (Throwable e) {<a name="line.169"></a>
<span class="sourceLineNo">170</span>                this.log.debug("caught exception closing open transaction during shutdown (ignoring)", e);<a name="line.170"></a>
<span class="sourceLineNo">171</span>            }<a name="line.171"></a>
<span class="sourceLineNo">172</span>        }<a name="line.172"></a>
<span class="sourceLineNo">173</span>    }<a name="line.173"></a>
<span class="sourceLineNo">174</span><a name="line.174"></a>
<span class="sourceLineNo">175</span>    /**<a name="line.175"></a>
<span class="sourceLineNo">176</span>     * Log specified exception. Used to ensure exceptions are logged at the point they are thrown.<a name="line.176"></a>
<span class="sourceLineNo">177</span>     *<a name="line.177"></a>
<span class="sourceLineNo">178</span>     * @param e exception to log<a name="line.178"></a>
<span class="sourceLineNo">179</span>     * @return e<a name="line.179"></a>
<span class="sourceLineNo">180</span>     */<a name="line.180"></a>
<span class="sourceLineNo">181</span>    protected KVTransactionException logException(KVTransactionException e) {<a name="line.181"></a>
<span class="sourceLineNo">182</span>        if (this.log.isDebugEnabled())<a name="line.182"></a>
<span class="sourceLineNo">183</span>            this.log.debug("throwing exception for " + e.getTransaction() + ": " + e);<a name="line.183"></a>
<span class="sourceLineNo">184</span>        return e;<a name="line.184"></a>
<span class="sourceLineNo">185</span>    }<a name="line.185"></a>
<span class="sourceLineNo">186</span><a name="line.186"></a>
<span class="sourceLineNo">187</span>    /**<a name="line.187"></a>
<span class="sourceLineNo">188</span>     * Wrap a {@link RuntimeException} as needed.<a name="line.188"></a>
<span class="sourceLineNo">189</span>     *<a name="line.189"></a>
<span class="sourceLineNo">190</span>     * &lt;p&gt;<a name="line.190"></a>
<span class="sourceLineNo">191</span>     * The implementation in {@link SnapshotKVDatabase} just returns {@code e}.<a name="line.191"></a>
<span class="sourceLineNo">192</span>     *<a name="line.192"></a>
<span class="sourceLineNo">193</span>     * @param tx transaction in which the exception occurred<a name="line.193"></a>
<span class="sourceLineNo">194</span>     * @param e original exception<a name="line.194"></a>
<span class="sourceLineNo">195</span>     * @return wrapped exception, or just {@code e}<a name="line.195"></a>
<span class="sourceLineNo">196</span>     */<a name="line.196"></a>
<span class="sourceLineNo">197</span>    protected RuntimeException wrapException(SnapshotKVTransaction tx, RuntimeException e) {<a name="line.197"></a>
<span class="sourceLineNo">198</span>        return e;<a name="line.198"></a>
<span class="sourceLineNo">199</span>    }<a name="line.199"></a>
<span class="sourceLineNo">200</span><a name="line.200"></a>
<span class="sourceLineNo">201</span>// Package methods<a name="line.201"></a>
<span class="sourceLineNo">202</span><a name="line.202"></a>
<span class="sourceLineNo">203</span>    /**<a name="line.203"></a>
<span class="sourceLineNo">204</span>     * Commit a transaction.<a name="line.204"></a>
<span class="sourceLineNo">205</span>     */<a name="line.205"></a>
<span class="sourceLineNo">206</span>    synchronized void commit(SnapshotKVTransaction tx) {<a name="line.206"></a>
<span class="sourceLineNo">207</span>        try {<a name="line.207"></a>
<span class="sourceLineNo">208</span>            this.doCommit(tx);<a name="line.208"></a>
<span class="sourceLineNo">209</span>        } finally {<a name="line.209"></a>
<span class="sourceLineNo">210</span>            this.cleanupTransaction(tx);<a name="line.210"></a>
<span class="sourceLineNo">211</span>        }<a name="line.211"></a>
<span class="sourceLineNo">212</span>    }<a name="line.212"></a>
<span class="sourceLineNo">213</span><a name="line.213"></a>
<span class="sourceLineNo">214</span>    /**<a name="line.214"></a>
<span class="sourceLineNo">215</span>     * Rollback a transaction.<a name="line.215"></a>
<span class="sourceLineNo">216</span>     */<a name="line.216"></a>
<span class="sourceLineNo">217</span>    synchronized void rollback(SnapshotKVTransaction tx) {<a name="line.217"></a>
<span class="sourceLineNo">218</span>        if (this.log.isDebugEnabled())<a name="line.218"></a>
<span class="sourceLineNo">219</span>            this.log.debug("rolling back transaction " + tx);<a name="line.219"></a>
<span class="sourceLineNo">220</span>        this.cleanupTransaction(tx);<a name="line.220"></a>
<span class="sourceLineNo">221</span>    }<a name="line.221"></a>
<span class="sourceLineNo">222</span><a name="line.222"></a>
<span class="sourceLineNo">223</span>// Internal methods<a name="line.223"></a>
<span class="sourceLineNo">224</span><a name="line.224"></a>
<span class="sourceLineNo">225</span>    private synchronized void doCommit(SnapshotKVTransaction tx) {<a name="line.225"></a>
<span class="sourceLineNo">226</span><a name="line.226"></a>
<span class="sourceLineNo">227</span>        // Get current and transaction's version info<a name="line.227"></a>
<span class="sourceLineNo">228</span>        final SnapshotVersion currentSnapshotVersion = this.getCurrentSnapshotVersion();<a name="line.228"></a>
<span class="sourceLineNo">229</span>        final SnapshotVersion transactionSnapshotVersion = tx.getSnapshotVersion();<a name="line.229"></a>
<span class="sourceLineNo">230</span>        final long transactionVersion = transactionSnapshotVersion.getVersion();<a name="line.230"></a>
<span class="sourceLineNo">231</span>        assert this.currentVersion - transactionVersion &gt;= 0;<a name="line.231"></a>
<span class="sourceLineNo">232</span>        assert transactionSnapshotVersion.getOpenTransactions().contains(tx);<a name="line.232"></a>
<span class="sourceLineNo">233</span><a name="line.233"></a>
<span class="sourceLineNo">234</span>        // Debug<a name="line.234"></a>
<span class="sourceLineNo">235</span>        if (this.log.isDebugEnabled()) {<a name="line.235"></a>
<span class="sourceLineNo">236</span>            this.log.debug("committing transaction " + tx + " based on version "<a name="line.236"></a>
<span class="sourceLineNo">237</span>              + transactionVersion + " (current version is " + this.currentVersion + ")");<a name="line.237"></a>
<span class="sourceLineNo">238</span>        }<a name="line.238"></a>
<span class="sourceLineNo">239</span><a name="line.239"></a>
<span class="sourceLineNo">240</span>        // Check whether transaction has been forcibly killed somehow<a name="line.240"></a>
<span class="sourceLineNo">241</span>        if (!transactionSnapshotVersion.getOpenTransactions().contains(tx))<a name="line.241"></a>
<span class="sourceLineNo">242</span>            throw this.logException(new RetryTransactionException(tx, "transaction has been forcibly invalidated"));<a name="line.242"></a>
<span class="sourceLineNo">243</span><a name="line.243"></a>
<span class="sourceLineNo">244</span>        // Get transaction reads &amp; writes<a name="line.244"></a>
<span class="sourceLineNo">245</span>        final Reads transactionReads = tx.getMutableView().getReads();<a name="line.245"></a>
<span class="sourceLineNo">246</span>        final Writes transactionWrites = tx.getMutableView().getWrites();<a name="line.246"></a>
<span class="sourceLineNo">247</span><a name="line.247"></a>
<span class="sourceLineNo">248</span>        // If the current version has advanced past the transaction's version, check for conflicts from intervening commits<a name="line.248"></a>
<span class="sourceLineNo">249</span>        for (long version = transactionVersion; version != this.currentVersion; version++) {<a name="line.249"></a>
<span class="sourceLineNo">250</span>            final SnapshotVersion committedSnapshotVersion = this.versionInfoMap.get(version);<a name="line.250"></a>
<span class="sourceLineNo">251</span>            final Writes committedWrites = committedSnapshotVersion.getCommittedWrites();<a name="line.251"></a>
<span class="sourceLineNo">252</span>            final boolean conflict = transactionReads.isConflict(committedWrites);<a name="line.252"></a>
<span class="sourceLineNo">253</span>            if (this.log.isDebugEnabled()) {<a name="line.253"></a>
<span class="sourceLineNo">254</span>                this.log.debug("ordering " + tx + " after writes in version " + version + " results in "<a name="line.254"></a>
<span class="sourceLineNo">255</span>                  + (conflict ? "conflict" : "no conflict"));<a name="line.255"></a>
<span class="sourceLineNo">256</span>                if (this.log.isTraceEnabled())<a name="line.256"></a>
<span class="sourceLineNo">257</span>                    this.log.trace("transaction reads: {} committed writes: {}", transactionReads, committedWrites);<a name="line.257"></a>
<span class="sourceLineNo">258</span>            }<a name="line.258"></a>
<span class="sourceLineNo">259</span>            if (conflict) {<a name="line.259"></a>
<span class="sourceLineNo">260</span>                throw this.logException(new RetryTransactionException(tx, "transaction is based on MVCC version "<a name="line.260"></a>
<span class="sourceLineNo">261</span>                  + transactionSnapshotVersion.getVersion() + " but the transaction committed at MVCC version "<a name="line.261"></a>
<span class="sourceLineNo">262</span>                  + version + " contains conflicting writes"));<a name="line.262"></a>
<span class="sourceLineNo">263</span>            }<a name="line.263"></a>
<span class="sourceLineNo">264</span>        }<a name="line.264"></a>
<span class="sourceLineNo">265</span><a name="line.265"></a>
<span class="sourceLineNo">266</span>        // Atomically apply the transaction's mutations<a name="line.266"></a>
<span class="sourceLineNo">267</span>        if (this.log.isDebugEnabled())<a name="line.267"></a>
<span class="sourceLineNo">268</span>            this.log.debug("applying mutations of " + tx + " to SnapshotMVCC database");<a name="line.268"></a>
<span class="sourceLineNo">269</span>        this.kvstore.mutate(transactionWrites, true);<a name="line.269"></a>
<span class="sourceLineNo">270</span><a name="line.270"></a>
<span class="sourceLineNo">271</span>        // Record transaction's writes for this version<a name="line.271"></a>
<span class="sourceLineNo">272</span>        currentSnapshotVersion.setCommittedWrites(transactionWrites);<a name="line.272"></a>
<span class="sourceLineNo">273</span><a name="line.273"></a>
<span class="sourceLineNo">274</span>        // Advance to the next MVCC version<a name="line.274"></a>
<span class="sourceLineNo">275</span>        if (this.log.isDebugEnabled())<a name="line.275"></a>
<span class="sourceLineNo">276</span>            this.log.debug("updating current version from " + this.currentVersion + " -&gt; " + (this.currentVersion + 1));<a name="line.276"></a>
<span class="sourceLineNo">277</span>        this.currentVersion++;<a name="line.277"></a>
<span class="sourceLineNo">278</span>    }<a name="line.278"></a>
<span class="sourceLineNo">279</span><a name="line.279"></a>
<span class="sourceLineNo">280</span>    private void cleanupTransaction(SnapshotKVTransaction tx) {<a name="line.280"></a>
<span class="sourceLineNo">281</span><a name="line.281"></a>
<span class="sourceLineNo">282</span>        // Debug<a name="line.282"></a>
<span class="sourceLineNo">283</span>        assert Thread.holdsLock(this);<a name="line.283"></a>
<span class="sourceLineNo">284</span>        if (this.log.isTraceEnabled())<a name="line.284"></a>
<span class="sourceLineNo">285</span>            this.log.trace("cleaning up transaction " + tx);<a name="line.285"></a>
<span class="sourceLineNo">286</span><a name="line.286"></a>
<span class="sourceLineNo">287</span>        // Remove open transaction from version<a name="line.287"></a>
<span class="sourceLineNo">288</span>        tx.getSnapshotVersion().removeOpenTransaction(tx);<a name="line.288"></a>
<span class="sourceLineNo">289</span><a name="line.289"></a>
<span class="sourceLineNo">290</span>        // Discard all versions older than all remaining open transactions<a name="line.290"></a>
<span class="sourceLineNo">291</span>        for (Iterator&lt;Map.Entry&lt;Long, SnapshotVersion&gt;&gt; i = this.versionInfoMap.entrySet().iterator(); i.hasNext(); ) {<a name="line.291"></a>
<span class="sourceLineNo">292</span>            final SnapshotVersion versionInfo = i.next().getValue();<a name="line.292"></a>
<span class="sourceLineNo">293</span>            if (!versionInfo.getOpenTransactions().isEmpty())<a name="line.293"></a>
<span class="sourceLineNo">294</span>                break;<a name="line.294"></a>
<span class="sourceLineNo">295</span>            if (this.log.isDebugEnabled())<a name="line.295"></a>
<span class="sourceLineNo">296</span>                this.log.debug("discarding obsolete version " + versionInfo);<a name="line.296"></a>
<span class="sourceLineNo">297</span>            final KVStore snapshot = versionInfo.getSnapshot();<a name="line.297"></a>
<span class="sourceLineNo">298</span>            if (snapshot instanceof AutoCloseable) {<a name="line.298"></a>
<span class="sourceLineNo">299</span>                try {<a name="line.299"></a>
<span class="sourceLineNo">300</span>                    ((AutoCloseable)snapshot).close();<a name="line.300"></a>
<span class="sourceLineNo">301</span>                } catch (Exception e) {<a name="line.301"></a>
<span class="sourceLineNo">302</span>                    // ignore<a name="line.302"></a>
<span class="sourceLineNo">303</span>                }<a name="line.303"></a>
<span class="sourceLineNo">304</span>            }<a name="line.304"></a>
<span class="sourceLineNo">305</span>            i.remove();<a name="line.305"></a>
<span class="sourceLineNo">306</span>        }<a name="line.306"></a>
<span class="sourceLineNo">307</span>    }<a name="line.307"></a>
<span class="sourceLineNo">308</span><a name="line.308"></a>
<span class="sourceLineNo">309</span>    // Get SnapshotVersion for the current MVCC version, creating on demand if necessary<a name="line.309"></a>
<span class="sourceLineNo">310</span>    private SnapshotVersion getCurrentSnapshotVersion() {<a name="line.310"></a>
<span class="sourceLineNo">311</span>        SnapshotVersion versionInfo = this.versionInfoMap.get(this.currentVersion);<a name="line.311"></a>
<span class="sourceLineNo">312</span>        if (versionInfo == null) {<a name="line.312"></a>
<span class="sourceLineNo">313</span>            versionInfo = new SnapshotVersion(this.currentVersion, this.kvstore.snapshot());<a name="line.313"></a>
<span class="sourceLineNo">314</span>            this.versionInfoMap.put(this.currentVersion, versionInfo);<a name="line.314"></a>
<span class="sourceLineNo">315</span>            if (this.log.isTraceEnabled())<a name="line.315"></a>
<span class="sourceLineNo">316</span>                this.log.trace("created new version " + versionInfo);<a name="line.316"></a>
<span class="sourceLineNo">317</span>        }<a name="line.317"></a>
<span class="sourceLineNo">318</span>        return versionInfo;<a name="line.318"></a>
<span class="sourceLineNo">319</span>    }<a name="line.319"></a>
<span class="sourceLineNo">320</span>}<a name="line.320"></a>
<span class="sourceLineNo">321</span><a name="line.321"></a>




























































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